A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's windings. A varying current in the first or primary winding creates a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or “voltage” in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary winding, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load.
A balun is a type of transformer that can convert electrical signals that are balanced about ground (differential) to signals that are unbalanced (single-ended) and vice versa. A balun can be formed by connecting one port of a transformer to ground. Baluns are also often used for impedance matching.
Transformers and baluns are commonly used in wireless communications. For example, transformers and baluns are frequently used in transceivers in wireless communication devices. Conventional coplanar interleaved transformers used in such applications have the primary and secondary windings interleaved on the same integrated circuit layer. The primary and secondary windings are constructed of planar metal traces. The number of turns in each of the primary and secondary windings determines the ratio of the voltages in the windings.
While conventional coplanar transformers reduce the size and resistance, they suffer from low quality (Q) factors. One-turn transformers exhibit a low K (coupling coefficient) for millimeter-Wave circuit applications (for example, in the frequency range of 30 GHz-300 GHz).
Additionally, transformers in advanced technology nodes (e.g., 90 nanometer, 65 nanometer, or smaller critical dimensions) have lower Fsr (resonance frequency) than larger technology nodes.
Improved transformers are desired.